(1) Field of the Invention
The present invention relates to a system for operating a variable vane in a gas turbine engine having improved wear characteristics and more particularly to a thrust washer constructed of electro-graphitic carbon for reducing wear used in said system.
(2) Description of the Related Art
In gas turbine engines, the variable vanes of the high pressure compressor are rotated via a trunnion assembly. With reference to FIG. 1, there is illustrated the construction of a portion of an engine including a trunnion 15. The trunnion 15 is situated between a liner housing 41 and an outer split case 22 and extends to a platform 21 through a thrust washer 23. Variable vane 17 is attached to the trunnion 15 via a vane platform 21.
In the past, the thrust washer 23 has been typically constructed of a wear resistant and low friction material such as graphite filled polyimide materials capable of continuous operation up to 650° F. The thrust washers 23 constructed of such polyimide materials are not capable of withstanding the high temperatures and loads of advanced high performance compressors. Potentially, this is a problem because it is necessary to avoid metal to metal contact between the vane platform 21 of the variable vane 17 and the outer split case 22. Such metal to metal contact could serve to degrade the vane platform 21 and the outer split case 22 and alter the physical geometry of each and induce higher friction in the variable vane kinematic system. Geometric alterations are undesirable because they can result in an undesirable angular displacement of the variable vane 17. Specifically, if a variable vane 17 is displaced with respect to adjacent vanes by more than 6°, a less than optimal operating scenario may be induced. It is therefore important that the vane platform 21 and the outer split case 22 operate in such a manner as to maintain their shapes, and, thus, maintain a constant variable vane angle.
What is therefore needed is a thrust washer which does not suffer material breakdown at high temperatures and which serves to maintain the fit and orientation of the vane platform 21 and the outer split case 22.